Feed-forward transformer models have driven rapid progress in 3D vision, but state-of-the-art methods such as VGGT and π3 have a computational cost that scales quadratically with the number of input images, making them inefficient when applied to large image collections. Sequential-reconstruction approaches reduce this cost but sacrifice reconstruction quality. We introduce ZipMap, a stateful feed-forward model that achieves linear-time, bidirectional 3D reconstruction while matching or surpassing the accuracy of quadratic-time methods. ZipMap employs test-time training layers to zip an entire image collection into a compact hidden scene state in a single forward pass, enabling reconstruction of over 700 frames in under 10 seconds on a single H100 GPU, more than 20× faster than state-of-the-art methods such as VGGT. Moreover, we demonstrate the benefits of having a stateful representation in real-time scene-state querying and its extension to sequential streaming reconstruction.
@article{arxiv.2603.04385,
title = {ZipMap: Linear-Time Stateful 3D Reconstruction via Test-Time Training},
author = {Haian Jin and Rundi Wu and Tianyuan Zhang and Ruiqi Gao and Jonathan T. Barron and Noah Snavely and Aleksander Holynski},
journal= {arXiv preprint arXiv:2603.04385},
year = {2026}
}